Electric thermostat for fire-alarms.



Patented Apr. :7, I900.

H. V. HAYES 8v. G. K. THOMPSON.

ELECTRIC THEBMUSTAT FUR FIRE ALARMS.

(Apfilication filed Aug. 10, 1899.)

(No Model.)

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UNITED STATES PATENT OFFICE.

HAMMOND V. HAYES, OF CAMBRIDGE, AND GEORGE K. THOMPSON, OF ALDEN, llIASSACHUSETTS, ASSIGNORS TO THE AMERICAN BELL TELEPHONE COMPANY, OF BOSTON, MASSACHUSETTS.

ELECTRIC THERMOSTAT FOR FIRE-ALARMS.

SPECIFICATION forming part of Letters Patent No. 647,565, dated April 17, 1900.

Application filed August 10, 1899. Serial No. 726,791. (No model.) V

T0 to whom it may concern.-

Be it known thatwe,HAMMOND V. HAYES, residing at Cambridge, and GEORGE K. THOMP- soN, residing at Walden, in the county of Middlesex and State of Massachusetts, have invented certain Improvements in Electric Thermostats for Fire-Alarms, of which the following is a specification.

The thermostat is of the cable form,in which two wire conductors normally out of electrical contact are adapted to complete an electric circuit containing the fire-alarm apparatus by the fusion of a third wire composed of metal melting at a required temperature. In our improved construction the two conducting-wires are insulated from each other and from the fusible wire by open-work non-conducting material surrounding one or both of the wires and all three wires in a bunch are surrounded by asbestos cloth, asbestos pa- 1 length of the fusible wire, and Fig. 4 shows a short length of the exterior covering of the cable.

The two conducting-wires are marked a 662. They are preferably of copper coated with tin. As shown, both are covered with an open-work braiding of insulating material I). Asbestos thread is the best material for such insulating material; but hard linen thread or cotton thread will answer the purpose, and it would also answer the purpose to cover but one of the conducting-wires with the braid. The fusible wire is marked a. As shown the imity may be adopted.

wires and the fusible wire thus insulated from each other are covered with a ribbon of asbestos paper at, wound in an overlapping cylindrical spiral or with any material not destructible by heat unless at a temperature far above that at which the material used for the fusible wirev melts. In the operation this outer covering holds the molten metal to which the fusible wire is reduced by heat until the molten metal penetrating the openwork insulation of the conducting-wires establishes an electrical connection between them. Asbestos thread makes the best insu lation, because there is no ash resulting there from when the fusible wire melts; but such ash as results from the combustion of cotton or linen thread does not materially interfere with the operation of the cable if the braiding is coarse in the sense that the openings between the threads are as large as possible consistent with normal good insulation.

It is unnecessary to show or describe electrio fire-alarm apparatus with which the cable embodying our invention as above described may be used.

We claim- 1. An electric thermostat, consisting of two conducting-wires and a wire of fusible mate rial covered with material not readily de- HAMMOND V. HAYES. GEORGE K. THOMPSON.

Witnesses:

GEO. WILLIS PIERCE, JOSEPH A. GATELY. 

